The present invention relates to a pipe joint and an apparatus for manufacturing pipe joint portions, and more particularly to a pipe joint in which a shape-retaining member which does not obstruct the flow of a fluid is inserted into a semirigid pipe made of a synthetic resin to partially expand the pipe and impart to the pipe a force which retaining it in the joint, and in which the pipe thereby prepared is attached to a joint body by means of a box nut, and to an apparatus for forming this type of pipe joint portion by inserting a shape-retaining member into the pipe to form an expanded portion.
Traditionally, a semirigid pipe made of a fluoroplastic which has a chemical-resistant properties and a high degree of lubricity is attached to a joint body in such a manner that a taper ring, such as one having a wedge-shaped cross-sectional configuration, is attached by a box nut to the outer periphery of an end of the pipe in which a groove is formed, and this ring is pressed against the peripheral surface of the pipe under pressure and is deformed by utilizing an inner slanting surface formed on the joint body and an upper inner surface of the box nut, thereby connecting the pipe to the joint body.
In this case, the taper ring is press-fitted to the pipe, but this joint does not display a large retaining force against tensile forces acting in the longitudinal direction of the pipe because the pipe is made of a synthetic resin such as a fluoroplastic and has a high degree of lubricity. Therefore, if the pipe or a device connected to this pipe by the joint is moved in the direction opposite to that in which the pipe and the joint body abut against each other so that a tensile force is applied thereto in this direction, there is the danger of a major accident occurring, caused by fluid flowing through the pipe being released by the disconnection of the pipe. Moreover, when the groove is formed on the pipe, a sufficient level of accuracy in finishing cannot always be obtained, and a reduction in the accuracy may result in a leak. There is also a possibility of the pipe being disconnected if the top end of the ring is deformed and disengaged from the groove by an extremely large tensile force, since this type of taper ring displays a low degree of mechanical strength.